The present invention relates to a wiper ring to be mounted to an end portion of a nut of a ball screw and also relates to a ball screw provided with such wiper ring.
Japanese Utility Model Laid-open Publication No. HEI 6-6795 disclosed such a wiper ring, in which one end side portion or entire portion of a wiper ring is divided into a plurality of segments or blocks in a circumferential direction thereof, and each of the segments is pressed towards radially center side by means of spring to thereby improve tightness between an inner peripheral portion of the wiper ring and a screw shaft disposed inside therein.
In such known art, in the structure in which only the one end side portion of the wiper ring is divided into a plurality of segments or blocks, there is usually formed a cutout portion, called “bias-cut”, at one portion of the wiper ring in its circumferential direction for separating the same. However, in an arrangement in which such wiper ring is mounted to a screw shaft, the bias-cut portion is widened (opened) and the inner peripheral portion of the wiper ring is deformed unwillingly in form of non-circular shape, and for this reason, at a portion opposite to the bias-cut forming portion of the wiper ring, the segment is closely contacted to the screw shaft. However, on the side of the bias-cut forming portion, the tightness of the segment to the screw shaft is made worse. As a result, sealing performance of the ball screw may be made different at various portions, thus being inconvenient.
On the other hand, the case where the entire portion of the wiper ring is divided into a plurality of segments or blocks will cause the following defective.
In such structure, when a gap is formed between adjacent two segments in the circumferential direction thereof, the gap may be widened when the segments are shifted. In such occasion, foreign material or like may easily invade and lubricant may easily leak through the widened gap. On the contrary, when the segments are contacted to each other in order to eliminate such gap, the movement of the respective segment towards the radially central portion of the segment due to such mutual contacting will be limited, which results in degradation of tightness between the segments and the screw shaft and deterioration of the sealing performance. Furthermore, in a case where any foreign material is clogged between the segment and the screw shaft, the segment is displaced towards the radially outer peripheral side against the force of the spring pressing the segment, and hence, the inner peripheral portion of the segment is separated from the screw shaft, thus deteriorating the sealing performance and hence being defective.